Composite detachment mechanisms

ABSTRACT

Described herein are composite detachment mechanisms for implantable devices and assemblies comprising these devices. Also provided are methods of using the detachment mechanisms and assemblies.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of co-pending U.S. patent applicationSer. No. 12/584,651, filed Sep. 9, 2009, which claims the benefit ofU.S. provisional patent application No. 61/191,456, filed Sep. 9, 2008,the disclosure of which is incorporated by reference in its entirety forall purposes.

FIELD OF THE INVENTION

This invention relates to composite detachment mechanisms forimplantable devices.

BACKGROUND

An aneurysm is a dilation of a blood vessel that poses a risk to healthfrom the potential for rupture, clotting, or dissecting. Rupture of an,aneurysm in the brain causes stroke, and rupture of an aneurysm in theabdomen causes shock. Cerebral aneurysms are usually detected inpatients as the result of a seizure or hemorrhage and can result insignificant morbidity or mortality.

There are a variety of materials and devices which have been used fortreatment of aneurysms, including platinum and stainless steel microcoils, polyvinyl alcohol sponges (Ivalone), and other mechanicaldevices. For example, vaso-occlusion devices are surgical implements orimplants that are placed within the vasculature of the human body,typically via a catheter, either to block the flow of blood through avessel making up that portion of the vasculature through the formationof an embolus or to form such an embolus within an aneurysm stemmingfrom the vessel. One widely used vaso-occlusive device is a helical wirecoil having windings that may be dimensioned to engage the walls of thevessels. (See, e.g., U.S. Pat. No. 4,994,069to Ritchart et al.).Variations of such devices include polymeric coatings or attachedpolymeric filaments have also been described. See, e.g., U.S. Pat. Nos.5,226,911; 5,935,145; 6,033,423; 6,280,457; 6,287,318; and 6,299,627. Inaddition, coil designs including stretch-resistant members that runthrough the lumen of the helical vaso-occlusive coil have also beendescribed. See, e.g., U.S. Pat. Nos. 5,582,619; 5,833,705; 5,853,418;6,004,338; 6,013,084; 6,179,857; and 6,193,728.

Typically, implantable devices include a detachment mechanism in orderto be released from the deployment mechanism (e.g., attached wire).Several classes of techniques have been developed to enable moreaccurate placement of implantable devices within a vessel. One classinvolves the use of electrolytic means to detach the vasoocclusivemember from the pusher. Electrolytic coil detachment is disclosed inU.S. Pat. Nos. 5,122,136; 5,354,295; 6,620,152; 6,425,893; and5,976,131, all to Guglielmi et al., describe electrolytically detachableembolic devices. U.S. Pat. No. 6,623,493 describes vaso-occlusive memberassembly with multiple detaching points. U.S. Pat. Nos. 6,589,236 and6,409,721 describe assemblies containing an electrolytically severablejoint. U.S. Patent Publication No. 20060271097A1 describes interlockingloop detachment junctions made of metal in which the loop proximal tothe implantable device is degraded by the application of energy, U.S.Patent Publication No. 20060271086A1 describes flexible detachmentjunctions formed by covering the implantable device and a deliverydevice with an articulating degradable polymer.

Other forms of energy are also used to sever sacrificial joints thatconnect pusher and vasoocclusive member apparatus. Sacrificialconnection member, preferably made from polyvinylacetate (PVA), reins,polymers, or shape memory alloys, can be used to join a conductive wireto a retention member. See, U.S. Pat. Nos. 5,759,161 and 5,846,210. Uponheating by a monopolar high frequency current, the sacrificialconnection member melts, severing the wire from the retention member.

U.S. Pat. No. 5,944,733 describes application of radiofrequency energyto sever a thermoplastic joint and U.S. Pat. No. 6,743,251 describespolymeric detachment joints that are severed by the application of lowfrequency energy or direct current. U.S. Pat. No. 6,346,091 describes awire detachment junction that is severed by application of vibrationalenergy.

In U.S. Pat. No. 4,735,201 to O'Reilly, an optical fiber is enclosedwithin a catheter and connected to a metallic tip on its distal end by alayer of hot-melt adhesive. The proximal end of the optical fiber isconnected to a laser energy source. When endovascularly introduced intoan aneurysm, laser energy is applied to the optical fiber, heating themetallic tip so as to cauterize the immediately surrounding tissue. Thelayer of hot-melt adhesive serving as the bonding material for theoptical fiber and metallic tip is melted during this lasing, but theintegrity of the interface is maintained by application of back pressureon the catheter by the physician. When it is apparent that the propertherapeutic effect has been accomplished, another pulse of laser energyis then applied to once again melt the hot-melt adhesive, but upon thisreheating the optical fiber and catheter are withdrawn by the physician,leaving the metallic tip in the aneurysm as a permanent plug. See, alsoU.S. Pat. No. 6,277,126.

Other methods for placing implantable devices within the vasculatureutilize heat releasable bonds that be detached by using laser energy(see, U.S. Pat. No. 5,108,407). EP 0992 220 describes an embolic coilplacement system which includes conductive wires running through thedelivery member. When these wires generate sufficient heat, they areable to sever the link between the embolic coil and the delivery wires.Further, U.S. Pat. No. 6,113,622 describes the use of fluid pressure(e.g., hydraulics) to detach an embolic coil.

However, there remains a need for composite detachment mechanisms asdescribed herein.

SUMMARY

Described herein are thermally activated composite detachment mechanismsmade of a polymer that melts upon thermal activation and a conductivematerial. When sufficient energy (e.g., electrical/thermal) is applied(via the conductive material) to the detachment mechanism, the polymermelts to an extent that the attached implantable device is released fromthe delivery mechanism into the vasculature.

In certain aspects, provided herein is an assembly comprising: animplantable device, and a composite detachment mechanism comprising apolymer and one or more conductive materials, wherein the compositedetachment mechanism is engaged (directly or indirectly) with theimplantable device until sufficient thermal energy is applied to thedetachment mechanism to allow disengagement of the implantable device totake place. The one or more conductive materials may be coated on thepolymer and/or the polymer may be coated onto the one or more conductivematerials.

In any of the assemblies described herein, the polymer may comprise alow melt polymer such as polyethylene (PE), poly-L-lactic acid (PLLA),polyglycolic acid (PGA), polyvinyl alcohol (PVA) and combinationsthereof. Similarly, the assemblies may comprise one or more layers ofthe conductive material, which may be for example, a metal (e.g.,nickel, iron chromium, tin, gold, platinum or combinations thereof). Incertain embodiment, the assembly comprises a single layer of one or moreconductive materials. In other embodiments, the assembly comprisesmultiple layers of two or more conductive materials.

In yet another aspect, any of the assemblies described herein mayfurther comprise an energy source (e.g., source of electrical or thermalenergy) operably connected to one or more electrodes in direct orindirect contact with the conductive material. In certain embodiments,the energy source comprises two electrodes, wherein the distal end ofthe electrodes comprise ring structures and wherein the ring structuresdirectly contact the conductive coating of the composite detachmentmechanism. The electrodes may contact a fabricated electrode assembly,for example a fabricated electrode assembly comprising an insulatinglayer positioned between two conductive layers; and a melt receptacleorifice spanning the insulating layer and at least part of theconductive layers, wherein the conductive material of the compositedetachment mechanism contacts the two conductive layers when engagedwith the implantable device.

In a still further aspect, any of the assemblies described herein mayfurther comprise a delivery device, for example, a catheter, a guidewire and/or a continuous conduit.

Any of assemblies described herein may further comprise one or moreinsulating materials, for example a single layer of insulatingmaterial(s) or multiple continuous or discontinuous layers of insulatingmaterial(s).

In any of the assemblies described herein, the implantable device maycomprise a vaso-occlusive device, for example a vaso-occlusive coil or atubular braid. The vaso-occlusive device may comprise one or more metalsand/or one or more polymers. In certain embodiments, the devicecomprises a metal selected from the group consisting of gold, platinum,tungsten, nickel, titanium and alloys thereof. In other embodiment, thevaso-occlusive device comprises a polymer, for example, the polymer iscoated onto a metal vaso-occlusive device.

In another aspect, described herein is a method of occluding a bodycavity, the method comprising introducing one or more of any of theimplantable assemblies described herein into the body cavity. In certainembodiments, the method comprises the steps of introducing animplantable assembly as described herein into the body cavity; andapplying sufficient energy to release the implantable device into thebody cavity, thereby occluding the body cavity. In certain embodiments,the body cavity is an aneurysm.

These and other embodiments will readily occur to those of skill in theart in light of the disclosure herein.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1A and FIG. 1B, are side views of exemplary assemblies comprising athermally detachable composite detachment mechanism as described herein.

FIG. 2 is an overview and partial cross-section of an exemplary assemblyas described herein comprising a composite thermally detachablemechanism.

FIG. 3 is a cross-section view of a micro fabricated electrode assembly.

DETAILED DESCRIPTION

Composite detachment mechanisms for implantable devices and assembliescomprising these detachment mechanisms are described. The detachmentmechanisms described herein find use in deploying vascular andneurovascular implants and are particularly useful in treatinganeurysms, for example small-diameter, curved or otherwise difficult toaccess vasculature, for example aneurysms, such as cerebral aneurysms.Methods of making and using these detachment mechanisms and assembliesare also described.

All publications, patents and patent applications cited herein, whetherabove or below, are hereby incorporated by reference in their entirety.

It must be noted that, as used in this specification and the appendedclaims, the singular forms “a”, “an”, and “the” include plural referentsunless the content clearly dictates otherwise.

The composite detachment mechanisms described herein include a meltablepolymer and a conductive material. Upon application of energy(electrical/thermal) via the conductive material, the polymer isdegraded (melted) and the implantable device detached from the deliverydevice.

Any polymer can be used in the detachment mechanisms described herein,including; but not limited to, polyethylene (PE), poly-L-lactic acid(PLLA), polyglycolic acid (PGA), polyvinyl alcohol (PVA), as well asother degradable polymers known to those of skill in the art. In apreferred embodiment, the polymer element comprises a low-meltingpolymer such as PE. The polymer element may comprise a single filamentand/or multiple filaments that are woven, braided and/or twisted aroundeach other.

Similarly, any conductive material can be used with the polymericelement in the composite detachment mechanisms described herein. Incertain embodiments, the conductive material comprises a metal, forexample nickel, iron, tin, chromium, gold, platinum, or combinationsthereof (e.g., NiCr, NiCrFe, SnO, Au and/or Pt). In certain embodiments,two or more layers of the same or different materials are used to formthe conductive material.

The conductive material may be combined with the polymer in any suitablefashion, including but not limited to, dip coating (continuous ordiscontinuous), sputter-coating, plating, use of adhesives, etc. Incertain embodiments, the polymer surrounds (e.g. is coated onto) aconductive material so as to form a meltable polymeric junction (e.g.,the substrate conductive material does not extend through the meltablejunction). In other embodiments, the conductive material is coated ontothe polymeric substrate in a continuous region. The conductive materialis selected such that passing a current through it results in heating totemperatures above the melting point of the polymeric element. At thepoint of melting, surface tension of the polymer melt will causeretraction and separation of the fiber into two separate pieces. Axiallystraining of the polymeric substrate (e.g., by operator pushing and/orpulling) may further facilitate the melting and separationeffectiveness.

Delivery mechanisms (e.g., catheter, delivery tube, guide wire systems,etc.) that allow for transmission of electrical energy are well known inthe art. Catheters with electrodes in the walls are described forexample in U.S. Pat. Nos. 6,059,779 and 7,020,516. Electrodes may alsobe transmitted through the lumen of the delivery mechanism. For example,bi-polar electrodes and/or anodes alone or twisted with a core wirecathode can also be used to supply current to the degradable detachmentmechanism.

Depicted in the appended drawings are exemplary embodiments of thepresent invention in which the implantable device is depicted as anembolic device. It will be appreciated that the drawings are forpurposes of illustration only and that other implantable devices can beused in place of embolic devices, for example, stents, filters, and thelike. Furthermore, although depicted in the Figures as embolic coils,the embolic devices may be of a variety of shapes or configurationincluding, but not limited to, braids, wires, knits, woven structures,tubes (e.g., perforated or slotted tubes), injection-molded devices andthe like. See, e.g., U.S. Pat. No. 6,533,801 and International PatentPublication WO 02/096273. It will also be appreciated that theassemblies can have various configurations as long as the requiredflexibility is present.

FIG. 1A and FIG. 1B, are side views of exemplary composite detachmentmechanism as described herein comprising at least one polymer and atleast one conductive material. FIG. 1A is a side end view of anexemplary polymer substrate 10 coated with a conductive material 20. Asshown, the coating can be continuous over a particular portion of thepolymer. FIG. 1B shows the reverse orientation in which a conductivematerial substrate 20 is coated with a meltable polymer 10.

FIG. 2 shows an exemplary assembly as described herein. The implantabledevice 30 is depicted as a vaso-occlusive coil (cross-section view). Thedetachment mechanism comprises polymer strands 10 and a conductivematerial 20 coating a portion of the polymer 10. Also shown areelectrodes 35, delivery device 45 and optional insulating electrodespacer 40.

In the embodiment depicted, electrodes 35 are configured as rings thatcontact the conductive material 20. It will be apparent that otherconfigurations are also possible including, but not limited to, linearelectrodes that terminate at (and are optionally attached to) theconductive material 20 of the detachment mechanism, hooked shapedelectrodes, combinations of rings, hooks, linear electrodes and thelike. Furthermore, configurations in which the electrodes are configuredto elevate and isolate the composite detachment mechanism and resultantmelt from other surfaces is preferred to help ensure better separation.

FIG. 3 shows across-section of an alternative embodiment in which theelectrode assembly is fabricated (micro-fabricated) to incorporate aninsulating layer 50, which allows electrical isolation between the twocontacts. In the embodiment shown, the micro fabricated assemblycomprises two electrodes (conductive wires) 35, each of which areelectrically connected 72 to each of the two conductive layers 55. Theelectrodes can be connected to the conductive layers in any wayincluding, but not limited, to soldering, adhesives, etc. Optionally,the composite detachment mechanism (polymer coated with conductivematerial) can be threaded through fiber threading cavity 60 and pulledtaught to fit within the detach fiber cavity 70 such that the conductivecoating 20 of the composite detachment mechanism bridges the distal gapand is in contact with both the conductive layers 55 of the fabricatedelectrode assembly.

Upon application of heat (electrical energy), the polymer fiber 10 ofthe composite detachment mechanism will melt into the melt receptacle 80and/or into the fiber threading cavity 60, which function as reservoirsto contain the melted polymer to prevent potential shorting of theconductive layers by the melt products. The melt receptacle 80 andthreading cavity 60 also provide additional surface area, which reducesor eliminates shorting in that the melted polymer has to coat an entirecontinuous area bridging both electrode gaps before a short occurs. Thesize and surface area of the melt receptacle can readily be determinedand adjusted by the skilled artisan depending on various factors, forexample, the thickness and volume of the polymer 10 to be melted.

In any of the embodiments described herein, one or more, preferably two,electrodes are typically employed. The polymer 10 component of thecomposite detachment mechanism is preferably attached to the implantabledevice in such away that when the composite portion of the detachmentmechanism is melted the device 10 and attached (severed) polymer 10 isreleased into the desired sites.

Thus, conductor element 35 will be any configuration and material thatallows for delivery of energy to melt the polymer 10 in the conductivematerial-coated region of the polymeric detachment mechanism. Forexample, the conductor element may comprise a conductive material suchas stainless steel, platinum, gold, etc. that is formed into a ringaround the composite detachment mechanism. Alternatively, the electrodemay be fabricated with conductive and insulating layers as well as amelt receptacle as shown in FIG. 3. Furthermore, although shown in theFigures as positioned in the lumen of the delivery device, it will beapparent that the conductor element(s) 35 can be positioned in thesidewalls of the selected delivery device 45.

The assemblies may also include an energy source which is preferablyconnected to the electrodes exterior to the subject's vasculature. Inaddition, the assemblies may include one or more actuators which allowthe operator to input the energy or to degrade (melt) the detachmentmechanism when deployment of the implant 30 is desired.

With regard to particular materials used in the implantable devices andassemblies of the invention, it is to be understood that the implantabledevices or assemblies may be made of a variety of materials, includingbut not limited to metals, polymers and combinations thereof, includingbut not limited to, stainless steel, platinum, kevlar, PET, carbothane,cyanoacrylate, epoxy, poly(ethyleneterephthalate) (PET),polytetrafluoroethylene (Teflon™), polypropylene, polyimidepolyethylene, polyglycolic acid, polylactic acid, nylon, polyester,fluoropolymer, and copolymers or combinations thereof. See, e.g., U.S.Pat. Nos. 6,585,754 and 6,280,457 for a description of various polymers.Different components of the devices and assemblies may be made ofdifferent materials.

In embodiments in which the implantable device comprises an emboliccoil, the main coil may be a coiled and/or braided structure comprisingone or more metals or metal alloys, for example, Platinum Group metals,especially platinum, rhodium, palladium, rhenium, as well as tungsten,gold, silver, tantalum, stainless steel and alloys of these metals.Preferably, the device comprises a material that maintains its shapedespite being subjected to high stress, for example, “super-elasticalloys” such as nickel/titanium alloys (48-58 atomic % nickel andoptionally containing modest amounts of iron); copper/zinc alloys (38-42weight % zinc); copper/zinc alloys containing 1-10 weight % of berylFum,silicon, tin, aluminum, or gallium; or nickel/aluminum alloys (36-38atomic % aluminum). Particularly preferred are the alloys described inU.S. Pat. Nos. 3,174,851; 3,351,463; and 3,753,700. Especially preferredis the titanium/nickel alloy known as “nitinol.” The main coil may alsocomprise a shape memory polymer such as those described in InternationalPublication WO 03/51444. The implantable device is preferablyelectrically insulated, for example, by coating a metallic coil (e.g.,stainless steel, platinum) with one or more electrically insulatingmaterials, for example one or more polymers such as polyimide.

The implantable device may also change shape upon release from thedeployment mechanism (e.g., pusher wire), for example change from alinear form to a relaxed, three-dimensional configuration upondeployment.

The devices described herein may also comprise additional components,such as co-solvents, plasticizers, coalescing solvents, bioactiveagents, antimicrobial agents, antithrombogenic agents (e.g., heparin),antibiotics, pigments, radio pacifiers and/or ion conductors which maybe coated using any suitable method or may be incorporated into theelement(s) during production. See, e.g., U.S. Pat. No. 6,585,754 and WO02/051460, U.S. Pat. No. 6,280,457. The additional components can becoated onto the device and/or can be placed in the vessel prior to,concurrently or after placement of one or more devices as describedherein.

The devices described herein are often introduced into a selected siteusing the procedure outlined below. This procedure may be used intreating a variety of maladies. For instance in the treatment of ananeurysm, the aneurysm itself will be filled (partially or fully) withthe compositions described herein.

Conventional catheter insertion and navigational techniques involvingguidewires or flow-directed devices may be used to access the site witha catheter. The mechanism will be such as to be capable of beingadvanced entirely through the catheter to place vaso-occlusive device atthe target site but yet with a sufficient portion of the distal end ofthe delivery mechanism protruding from the distal end of the catheter toenable detachment of the implantable vaso-occlusive device. For use inperipheral or neural surgeries, the delivery mechanism will normally beabout 100-200 cm in length, more normally 130-180 cm in length. Thediameter of the delivery mechanism is usually in the range of 0.25 toabout 0.90 mm. Briefly, occlusive devices (and/or additional components)described herein are typically loaded into a carrier for introductioninto the delivery catheter and introduced to the chosen site using theprocedure outlined below. This procedure may be used in treating avariety of maladies. For instance, in treatment of an aneurysm, theaneurysm itself may be filled with the embolics (e.g. vaso-occlusivemembers and/or liquid embolics and bioactive materials) which causeformation of an emboli and, at some later time, is at least partiallyreplaced by neovascularized collagenous material formed around theimplanted vaso-occlusive devices.

A selected site is reached through the vascular system using acollection of specifically chosen catheters and/or guide wires. It isclear that should the site be in a remote site, e.g., in the brain,methods of reaching this site are somewhat limited. One widely acceptedprocedure is found in U.S. Pat. No. 4,994,069 to Ritchart, et al. Itutilizes a fine endovascular catheter such as is found in U.S. Pat. No.4,739,768, to Engelson. First of all, a large catheter is introducedthrough an entry site in the vasculature. Typically, this would bethrough a femoral artery in the groin, Other entry sites sometimeschosen are found in the neck and are in general well known by physicianswho practice this type of medicine. Once the introducer is in place, aguiding catheter is then used to provide a safe passageway from theentry site to a region near the site to be treated. For instance, intreating a site in the human brain, a guiding catheter would be chosenwhich would extend from the entry site at the femoral artery, up throughthe large arteries extending to the heart, around the heart through theaortic arch, and downstream through one of the arteries extending fromthe upper side of the aorta. A guidewire and neurovascular catheter suchas that described in the Engelson patent are then placed through theguiding catheter. Once the distal end of the catheter is positioned atthe site, often by locating its distal end through the use of radiopaquemarker material and fluoroscopy, the catheter is cleared and/or flushedwith an electrolyte solution.

Once the selected site has been reached, the vaso-occlusive device isextrude by application of energy which degrades (melts) the polymercomponent of the detachment mechanisms as described herein. Upon meltingof the polymer component, the implantable device is released in thedesired position of the selected site.

Modifications of the procedures and assemblies described above, and themethods of using them in keeping with this disclosure will be apparentto those having skill in this mechanical and surgical art. Thesevariations are intended to be within the scope of the claims thatfollow.

What is claimed:
 1. An assembly for delivering an implantable device ina body, comprising: an implantable device; an electrode assemblycomprising: a first conductive layer, a second conductive layer, and aninsulating layer disposed between the first and second conductivelayers, wherein the first conductive layer, second conductive layer andinsulating layer define a cavity; a delivery device, with first andsecond electrically conductive members extending distally from thedelivery device, the first and second electrically conductive memberselectrically connected to the first and second conductive layers,respectively, of the electrode assembly; and a composite detachmentmechanism comprising a polymer strand secured to the implantable device,the polymer strand comprising a detachment portion coated with anelectrically conductive material and extending through the cavity of theelectrode assembly.
 2. The assembly of claim 1, wherein the cavitycomprises a threading cavity, a detach cavity and a melt receptacle. 3.The assembly of claim 2, wherein the threading cavity is dimensioned toreceive the polymer strand such that the electrically conductive coatingmaterial does not conduct energy from the first electrically conductivemember to the second electrically conductive member.
 4. The assembly ofclaim 2, wherein the detach cavity is dimensioned to receive the polymerstrand such that energy is conducted from the first electricallyconductive member to the second electrically conductive member via theelectrically conductive coating material to heat and melt the detachmentportion of the polymer strand to release the implantable device from thedelivery device.
 5. Then assembly of claim 4, wherein the meltreceptacle receives the melted polymer of the polymer strand.
 6. Theassembly of claim 1, wherein the polymer comprises a low melt polymer.7. The assembly of claim 6, wherein the low melt polymer is selectedfrom the group consisting of polyethylene (PE), poly-L-lactic acid(PLLA), polyglycolic acid (PGA), polyvinyl alcohol (PVA) andcombinations thereof.
 8. The assembly of claim 6, wherein theimplantable device comprises a vaso-occlusive device.
 9. The assembly ofclaim 8, wherein the vaso-occlusive device is a coil or a tubular braid.10. The assembly of claim 8, wherein the vaso-occlusive device comprisesa metal.
 11. The assembly of claim 10, wherein the metal is selectedfrom the group consisting of gold, tungsten, nickel, titanium and alloysthereof.
 12. The assembly of claim 8, wherein the vaso-occlusive devicecomprises a polymer.
 13. The assembly of claim 12, wherein thevaso-occlusive device comprises a metal and the polymer is coated ontothe metal vaso-occlusive device.
 14. The assembly of claim 1, whereinthe conductive coating material comprises nickel, iron chromium, tin,gold, platinum or combinations thereof.
 15. The assembly of claim 1,wherein the conductive coating comprises a single layer of one or moreconductive materials.
 16. The assembly of claim 1, wherein theconductive coating comprises multiple layers of two or more conductivematerials.
 17. The assembly of claim 1, further comprising an energysource operably connected to the first and second conductive members.18. The assembly of claim 1, wherein the delivery device comprises acatheter, guide wire, or a continuous conduit.
 19. The assembly of claim1, further comprising an insulating device.